We have in the past carried out parts of three separate investigations on this grant. One of these has been concerned with studies relating to fatty acids, another to cholesterol, and the last to carotenes. However, our studies on the biosynthesis of fatty acids have expanded very much during the past two to three years. Hence, most of our effort on this grant is now concentrated on studies related to fatty acid synthesis. These studies are concerned with the structural organization of the fatty acid synthetase by a cell-free system. We have recently separated the half-molecular weight, nonidentical subunits of several fatty acid synthetase complexes. Hence, we are now attempting to dissociate these subunits to invidual proteins. If we are successful, we will then separate these components and identify their properties and the mechanisms of the reactions catalyzed by each. We have recently also shown that pigeon liver fatty acid synthetase complex is comprimised of three separable species (apo-, hola-a and holo-b fatty acid synthetases). We are now attempting to determine the mechanisms of control over the proportions of these components in the liver cell and whether this is the short-term mechanism of regulating the rate of fatty acid synthesis in avian and mammalian liver. The final study is concerned with the identification of the factors that control the rate of synthesis of pigeon liver fatty acid synthetase in a cell-free system. Attempts are also being made to isolate the mRNA coding for the fatty acid synthetase complex in pigeon liver. Bibliographic references: Muesing, R.A., and Porter, J. W. (1975) in Methods in Enzymology, J.M. Lowenstein, Ed., Vol.35, pp. 45-49. Academic Press, New York. Pigeon Liver Fatty Acid Synthetase. Katiyar, S.S., Cleland, W.W., and Porter, J.W. (1975) J. Biol. Chem. 250, 2709-2717. Fatty acid synthetase: A steady state kinetic analysis of the reaction catalyzed by the enzyme from pigeon liver.